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Diffstat (limited to 'std/src/macros.rs')
| -rw-r--r-- | std/src/macros.rs | 394 |
1 files changed, 394 insertions, 0 deletions
diff --git a/std/src/macros.rs b/std/src/macros.rs new file mode 100644 index 0000000..a9b4336 --- /dev/null +++ b/std/src/macros.rs @@ -0,0 +1,394 @@ +// Copyright 2014 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +/// The entry point for panic of Rust threads. +/// +/// This macro is used to inject panic into a Rust thread, causing the thread to +/// panic entirely. Each thread's panic can be reaped as the `Box<Any>` type, +/// and the single-argument form of the `panic!` macro will be the value which +/// is transmitted. +/// +/// The multi-argument form of this macro panics with a string and has the +/// `format!` syntax for building a string. +/// +/// # Examples +/// +/// ```should_panic +/// # #![allow(unreachable_code)] +/// panic!(); +/// panic!("this is a terrible mistake!"); +/// panic!(4); // panic with the value of 4 to be collected elsewhere +/// panic!("this is a {} {message}", "fancy", message = "message"); +/// ``` +#[macro_export] +#[allow_internal_unstable] +macro_rules! panic { + () => ({ + panic!("explicit panic") + }); + ($msg:expr) => ({ + $crate::rt::begin_panic($msg, { + // static requires less code at runtime, more constant data + static _FILE_LINE: (&'static str, u32) = (file!(), line!()); + &_FILE_LINE + }) + }); + ($fmt:expr, $($arg:tt)+) => ({ + $crate::rt::begin_panic_fmt(&format_args!($fmt, $($arg)+), { + // The leading _'s are to avoid dead code warnings if this is + // used inside a dead function. Just `#[allow(dead_code)]` is + // insufficient, since the user may have + // `#[forbid(dead_code)]` and which cannot be overridden. + static _FILE_LINE: (&'static str, u32) = (file!(), line!()); + &_FILE_LINE + }) + }); +} + +/// Ensure that a boolean expression is `true` at runtime. +/// +/// This will invoke the `panic!` macro if the provided expression cannot be +/// evaluated to `true` at runtime. +/// +/// This macro has a second version, where a custom panic message can be provided. +/// +/// # Examples +/// +/// ``` +/// // the panic message for these assertions is the stringified value of the +/// // expression given. +/// assert!(true); +/// +/// fn some_computation() -> bool { true } // a very simple function +/// +/// assert!(some_computation()); +/// +/// // assert with a custom message +/// let x = true; +/// assert!(x, "x wasn't true!"); +/// +/// let a = 3; let b = 27; +/// assert!(a + b == 30, "a = {}, b = {}", a, b); +/// ``` +#[macro_export] +macro_rules! assert { + ($cond:expr) => ( + if !$cond { + panic!(concat!("assertion failed: ", stringify!($cond))) + } + ); + ($cond:expr, $($arg:tt)+) => ( + if !$cond { + panic!($($arg)+) + } + ); +} + +/// Asserts that two expressions are equal to each other. +/// +/// On panic, this macro will print the values of the expressions with their +/// debug representations. +/// +/// # Examples +/// +/// ``` +/// let a = 3; +/// let b = 1 + 2; +/// assert_eq!(a, b); +/// ``` +#[macro_export] +macro_rules! assert_eq { + ($left:expr , $right:expr) => ({ + match (&$left, &$right) { + (left_val, right_val) => { + if !(*left_val == *right_val) { + panic!("assertion failed: `(left == right)` \ + (left: `{:?}`, right: `{:?}`)", left_val, right_val) + } + } + } + }) +} + +/// Ensure that a boolean expression is `true` at runtime. +/// +/// This will invoke the `panic!` macro if the provided expression cannot be +/// evaluated to `true` at runtime. +/// +/// Like `assert!`, this macro also has a second version, where a custom panic +/// message can be provided. +/// +/// Unlike `assert!`, `debug_assert!` statements are only enabled in non +/// optimized builds by default. An optimized build will omit all +/// `debug_assert!` statements unless `-C debug-assertions` is passed to the +/// compiler. This makes `debug_assert!` useful for checks that are too +/// expensive to be present in a release build but may be helpful during +/// development. +/// +/// # Examples +/// +/// ``` +/// // the panic message for these assertions is the stringified value of the +/// // expression given. +/// debug_assert!(true); +/// +/// fn some_expensive_computation() -> bool { true } // a very simple function +/// debug_assert!(some_expensive_computation()); +/// +/// // assert with a custom message +/// let x = true; +/// debug_assert!(x, "x wasn't true!"); +/// +/// let a = 3; let b = 27; +/// debug_assert!(a + b == 30, "a = {}, b = {}", a, b); +/// ``` +#[macro_export] +macro_rules! debug_assert { + ($($arg:tt)*) => (if cfg!(debug_assertions) { assert!($($arg)*); }) +} + +/// Asserts that two expressions are equal to each other. +/// +/// On panic, this macro will print the values of the expressions with their +/// debug representations. +/// +/// Unlike `assert_eq!`, `debug_assert_eq!` statements are only enabled in non +/// optimized builds by default. An optimized build will omit all +/// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the +/// compiler. This makes `debug_assert_eq!` useful for checks that are too +/// expensive to be present in a release build but may be helpful during +/// development. +/// +/// # Examples +/// +/// ``` +/// let a = 3; +/// let b = 1 + 2; +/// debug_assert_eq!(a, b); +/// ``` +#[macro_export] +macro_rules! debug_assert_eq { + ($($arg:tt)*) => (if cfg!(debug_assertions) { assert_eq!($($arg)*); }) +} + +/// Helper macro for unwrapping `Result` values while returning early with an +/// error if the value of the expression is `Err`. Can only be used in +/// functions that return `Result` because of the early return of `Err` that +/// it provides. +/// +/// # Examples +/// +/// ``` +/// use std::io; +/// use std::fs::File; +/// use std::io::prelude::*; +/// +/// fn write_to_file_using_try() -> Result<(), io::Error> { +/// let mut file = try!(File::create("my_best_friends.txt")); +/// try!(file.write_all(b"This is a list of my best friends.")); +/// println!("I wrote to the file"); +/// Ok(()) +/// } +/// // This is equivalent to: +/// fn write_to_file_using_match() -> Result<(), io::Error> { +/// let mut file = try!(File::create("my_best_friends.txt")); +/// match file.write_all(b"This is a list of my best friends.") { +/// Ok(v) => v, +/// Err(e) => return Err(e), +/// } +/// println!("I wrote to the file"); +/// Ok(()) +/// } +/// ``` +#[macro_export] +macro_rules! try { + ($expr:expr) => (match $expr { + $crate::result::Result::Ok(val) => val, + $crate::result::Result::Err(err) => { + return $crate::result::Result::Err($crate::convert::From::from(err)) + } + }) +} + +/// Use the `format!` syntax to write data into a buffer. +/// +/// This macro is typically used with a buffer of `&mut `[`Write`][write]. +/// +/// See [`std::fmt`][fmt] for more information on format syntax. +/// +/// [fmt]: ../std/fmt/index.html +/// [write]: ../std/io/trait.Write.html +/// +/// # Examples +/// +/// ``` +/// use std::io::Write; +/// +/// let mut w = Vec::new(); +/// write!(&mut w, "test").unwrap(); +/// write!(&mut w, "formatted {}", "arguments").unwrap(); +/// +/// assert_eq!(w, b"testformatted arguments"); +/// ``` +#[macro_export] +macro_rules! write { + ($dst:expr, $($arg:tt)*) => ($dst.write_fmt(format_args!($($arg)*))) +} + +/// Use the `format!` syntax to write data into a buffer, appending a newline. +/// +/// This macro is typically used with a buffer of `&mut `[`Write`][write]. +/// +/// See [`std::fmt`][fmt] for more information on format syntax. +/// +/// [fmt]: ../std/fmt/index.html +/// [write]: ../std/io/trait.Write.html +/// +/// # Examples +/// +/// ``` +/// use std::io::Write; +/// +/// let mut w = Vec::new(); +/// writeln!(&mut w, "test").unwrap(); +/// writeln!(&mut w, "formatted {}", "arguments").unwrap(); +/// +/// assert_eq!(&w[..], "test\nformatted arguments\n".as_bytes()); +/// ``` +#[macro_export] +macro_rules! writeln { + ($dst:expr, $fmt:expr) => ( + write!($dst, concat!($fmt, "\n")) + ); + ($dst:expr, $fmt:expr, $($arg:tt)*) => ( + write!($dst, concat!($fmt, "\n"), $($arg)*) + ); +} + +/// A utility macro for indicating unreachable code. +/// +/// This is useful any time that the compiler can't determine that some code is unreachable. For +/// example: +/// +/// * Match arms with guard conditions. +/// * Loops that dynamically terminate. +/// * Iterators that dynamically terminate. +/// +/// # Panics +/// +/// This will always panic. +/// +/// # Examples +/// +/// Match arms: +/// +/// ``` +/// # #[allow(dead_code)] +/// fn foo(x: Option<i32>) { +/// match x { +/// Some(n) if n >= 0 => println!("Some(Non-negative)"), +/// Some(n) if n < 0 => println!("Some(Negative)"), +/// Some(_) => unreachable!(), // compile error if commented out +/// None => println!("None") +/// } +/// } +/// ``` +/// +/// Iterators: +/// +/// ``` +/// # #[allow(dead_code)] +/// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3 +/// for i in 0.. { +/// if 3*i < i { panic!("u32 overflow"); } +/// if x < 3*i { return i-1; } +/// } +/// unreachable!(); +/// } +/// ``` +#[macro_export] +macro_rules! unreachable { + () => ({ + panic!("internal error: entered unreachable code") + }); + ($msg:expr) => ({ + unreachable!("{}", $msg) + }); + ($fmt:expr, $($arg:tt)*) => ({ + panic!(concat!("internal error: entered unreachable code: ", $fmt), $($arg)*) + }); +} + +/// A standardized placeholder for marking unfinished code. It panics with the +/// message `"not yet implemented"` when executed. +/// +/// This can be useful if you are prototyping and are just looking to have your +/// code typecheck, or if you're implementing a trait that requires multiple +/// methods, and you're only planning on using one of them. +/// +/// # Examples +/// +/// Here's an example of some in-progress code. We have a trait `Foo`: +/// +/// ``` +/// trait Foo { +/// fn bar(&self); +/// fn baz(&self); +/// } +/// ``` +/// +/// We want to implement `Foo` on one of our types, but we also want to work on +/// just `bar()` first. In order for our code to compile, we need to implement +/// `baz()`, so we can use `unimplemented!`: +/// +/// ``` +/// # trait Foo { +/// # fn bar(&self); +/// # fn baz(&self); +/// # } +/// struct MyStruct; +/// +/// impl Foo for MyStruct { +/// fn bar(&self) { +/// // implementation goes here +/// } +/// +/// fn baz(&self) { +/// // let's not worry about implementing baz() for now +/// unimplemented!(); +/// } +/// } +/// +/// fn main() { +/// let s = MyStruct; +/// s.bar(); +/// +/// // we aren't even using baz() yet, so this is fine. +/// } +/// ``` +#[macro_export] +macro_rules! unimplemented { + () => (panic!("not yet implemented")) +} + +#[macro_export] +#[allow_internal_unstable] +macro_rules! print { + ($($arg:tt)*) => ( + $crate::io::_print(format_args!($($arg)*)); + ); +} + +#[macro_export] +macro_rules! println { + () => (print!("\n")); + ($fmt:expr) => (print!(concat!($fmt, "\n"))); + ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*)); +} |